1. Field of the Invention
The present invention relates generally to cryogenic hybrid rocket engines and propellant combinations, and more particularly to a hybrid rocket engine utilizing a grain of "solid" fluid that is normally a liquid or gaseous fluid at room temperature at atmospheric pressure in combination with a fluid propellant. The invention also relates generally to a method of propelling a rocket utilizing a solid propellant and a liquid or gaseous propellant in an engine form commonly referred to as a hybrid rocket engine and a method of forming the solid propellant grain in such an engine.
2. Description of the Prior Art
Conventional hybrid rocket engines comprise, by definition, a grain of a solid propellant and a separate liquid propellant. These engines commonly comprise a solid fuel or propellant which is in its solid state at room temperature in combination with a second propellant in a liquid or fluid state. One problem with previous hybrid engines is that the choice of propellants for the solid grain has been limited to chemicals that are solid at room temperature. These chemicals do not produce high thrust per unit of mass flow and accordingly are classed as low performance propellants. A need exists for providing high-performing cryogenic propellants in their solid form in a hybrid rocket engine. A problem with this, however, is how to deliver the solid propellant in solid form, to the combustion chamber and how to maintain the solid propellant, which is gaseous or liquid at room temperature, in its solid form as well as to maintain the liquid propellant at its desired temperature. A further problem is that propellants commonly used for existing hybrid rocket propellant grains do not have the ability to capture and retain highly energetic atoms, or free-radicals or energetic molecules that impart significant energy density benefits to rocket performance. Propellant grains that have the ability to capture such high energy density materials (HEDMs) are needed to improve performance of hybrid rockets for low-cost access to space.
Accordingly, there is a need in the art for an improved cryogenic hybrid rocket engine which avoids or minimizes the above problems, captures the desired new capabilities and simplifies the engine structure.